I'm not a Muun wallet user, but I'm interested in any responses to your note. Are you experiencing problems with the current mempool backlog perhaps? What lightning tx issues with Muun?
Discussion
Last I checked, Muun was using on-chain transactions with every LN transaction and for small LN transactions, they loaned sats to the users as paying 500sat in fees to send 12sat wouldn't be too welcome by most.